The present invention relates generally to tobacco products and more particularly to an improved cohesive tobacco composition in which tobacco pectins within the tobacco itself serve as the binder, a process for making the composition, and the production of tobacco sheet from such composition.
During the production and processing of tobacco products, including aging, blending, sheet forming, cutting, drying, cooling, screening, shaping and packaging, considerable amounts of tobacco fines, dust, stems, and other small tobacco plant parts are produced. It is known that such small tobacco plant parts can be combined with a binder to form a coherent sheet, which resembles leaf tobacco and which is commonly referred to as reconstituted tobacco.
It is also known to treat the small tobacoo plant parts to release tobacco pectins from within the tobacco itself and to use such pectins as the binder. Such processes are taught by U.S. Pat. Nos. 3,353,541 and 3,420,241 to Hind and Seligman, U.S. Pat. No. 3,386,449 to Hind, and U.S. Pat. No. 3,760,815 to Deszyck, the disclosures of which are incorporated herein by reference. Unlike reconstituted tobacco made with non-tobacco derived binders, the reconstituted tobacco which is obtained from such pectin release processes need not contain any added cellulose or proteinaceous material which is foreign to tobacco, since the binder which is employed may be derived solely from tobacco, and may be produced in such a manner that it contains no materials other than those which naturally occur in tobacco. Thus, reconstituted tobacco produced in accordance with these processes can be so formulated as to be similar to natural tobacco in physical properties and chemical composition.
In the '541, '241 and '449 patents, diammonium acid phosphate or ammonium orthophosphate, is employed to treat the tobacco plant parts to destroy the alkaline earth metal cross-links of the tobacco pectins. The mechanism of the process involves four distinct steps: (1) the penetration of the tobacco material by the cross-link destruction agents; (2) the destruction of the alkaline earth metal cross-links and the release of the tobacco pectins; (3) the solubilization and migration of the resulting tobacco pectins from the interstices of the tobacco material; and (4) the depositing of the released tobacco pectins on the surface of the treated plant parts.
The first step of penetration of the tobacco material by the cross-link destruction agent begins upon contact of the tobacco material with the destruction agent in an aqueous mixture. Considering a single tobacco particle, the agent in aqueous form soaks into and permeates the particle over some period of time which may depend on such factors as the temperature of the mixture and the size, shape, surface area and porosity of the particles. Considering a large quantity of dry tobacco particles to be combined with an aqueous solution of pectin release agent, the time required to complete this step is increased by the mixing time required to effect contact of essentially every individual tobacco particle with the solution. Essentially complete mixing is highly desirable, for if not achieved, the result is an unacceptable sheet material containing lumps of dry tobacco. Reconstituted tobacco containing such lumps exhibit lower tensile strength and inferior appearance.
Similarly, if one begins with a mixture of dry tobacco particles and dry cross-link destruction agent to be combined with an aqueous solution to initiate the permeation, the mixing time must be sufficient to accommodate the additional time involved in dissolving the dry cross-link destruction agent into solution prior to permeation of the tobacco particles thereby.
The second step, which is release of the tobacco pectins by destruction of the alkaline earth metal cross-links, can be considered to occur somewhat concurrently with the first. As the agent permeates portions of the tobacco particles, destruction of the cross-links begins in those permeated portions.
The third step, which is solubilization of the resulting tobacco pectins and migration thereof from the interstices of the tobacco particles, involves a migration of the pectins in opposite directions to the directions of migration or permeation of the first step and thus must occur over some time period subsequent to the first step.
The fourth step, which is depositing the released tobacco pectins on the surface of the treated tobacco particles, can be considered to occur somewhat concurrently with the third. As the tobacco pectin migrates out of a tobacco particle, it may deposit onto the particle surface or dissolve into the solution and be deposited onto other particles.
In the process according to the '815 patent, ammonium salts of organic acids are used as the cross-link destruction agent. However, the steps of the mechanism are essentially the same as described above.
Under the conditions of the '541 process such as temperature, solids content, pH and mixture proportions, agitating or stirring of the mixture is taught therein as required for about one minute to one day. Under the conditions of the '815 process one-half to twenty-four hours is required. For economic reasons, it is desirable to reduce the time of agitation to a minimum, however, sufficient time must be allowed for the steps of the process to occur.
During long agitation times, conditions such as temperature and pH may change, thus means must be provided for monitoring and controlling these conditions. Moreover, long agitation times may increase viscosity to unacceptable levels such that the composition may not be cast, sprayed, coated, extruded or otherwise used in the manufacture of a tobacco product. Accordingly, the viscosity of the composition must be reduced to an acceptable value prior to its utilization. Typically, viscosity reduction is accomplished by dilution. However, such dilution increases the drying load and greatly impacts the economics of the process. In the '241 patent viscosity is kept at acceptable values by dilution with water prior to agitation. Water to a certain extent is required in any slurry making process, however, the less water used, and therefore the higher solids content of the resulting composition, the lower the drying load and the more favorable the economics of the process. As a result of the dilution factor, the slurry solids content of the process of the '241 patent are in the range of about 5% to 10%. A high solids content, greater than about 14 percent, is desirable. Also, with long agitation times mixing and storage vats may become necessary. The employment of such equipment adds significantly to the capital, maintenance and operating costs of the process.
In one known method of producing a cohesive tobacco composition as described in U.S. Pat. No. 4,325,391, incorporated herein by reference, tobacco material and an aqueous adhesive material are first contacted together and mixed within a high intensity mixer. In the '391 process, mixing times of an order of magnitude less than one minute and slurry solids content of about 22% are achieved. In such a quick mixing process, insufficient time elapses for the tobacco material to be thoroughly permeated by the aqueous adhesive material. In processes such as the '391 process wherein an adhesive is added to rather than produced within the mixture, this is not only an acceptable result but also a desirable one because permeation is not required since only an application of the adhesive to the surface of the tobacco material is necessary for binding the tobacco particles together in the formation of the tobacco sheet or other tobacco product. Moreover, as taught in the '391 patent, permeation is undesirable in such an adhesive additive process because subsequently greater drying capacity is required to dry the tobacco sheet or other tobacco product to an acceptable moisture content and thereby effect the adherence of the tobacco particles to one another. Indeed, the objective of the '391 patent is to effect sheet formation prior to complete moisture permeation and equilibrium of the tobacco particle.
Conversely, in processes for producing a cohesive tobacco composition whereby the tobacco pectin is released from the tobacco particles and used as the adhesive, permeation of the cross-link destruction agent is absolutely essential to effect release of the tobacco pectin adhesive. Moreover, as taught in the '541 patent, heretofore a period of one minute to one day of agitation and mixing was required for this to occur.
Accordingly, there is a need in the art for a process of making a cohesive tobacco composition and a reconstituted tobacco which has the advantages of using natural adhesive released from the tobacco itself, which yields a composition with increased solids content and acceptable viscosity and which may be accomplished quickly enough to avoid the expense of mixing tubs and holding tanks and the like.